A disc grinder is used, for example, to perform a grinding by rotating a tool bit thereof by means of a motor as a driving source. Grindstone, diamond wheel or the like is used as the tool bit. During the grinding operation, the tool bit of the disc grinder is partially covered with a wheel guard for safety measures.
FIG. 9 is a top plan view of a related-art wheel guard unit. As shown in FIG. 9, the related-art wheel guard unit is provided with a semicircular wheel guard 1 configured to cover approximately a half of a disc-shaped tool bit B and a fastening band 3. The fastening band 3 includes a half ring-shaped member 3A fixed to or formed integrally with the wheel guard 1 and another half ring-shaped member 3B configured to be separated from the half ring-shaped member 3A.
In the wheel guard unit shown in FIG. 9, one end of a manipulation lever 2 is pivotably attached, by means of a screw 4, to a lever holder 10 coupled to the wheel guard 1. A cam part is formed at a proximal end portion of the manipulation lever 2. The cam part is engaged with a bent portion 3b2 of the half ring-shaped member 3B of the fastening band 3. A screw 6 is inserted through another bent portion 3b1 of the half ring-shaped member 3B and a bent portion 3a of the half ring-shaped member 3A, and the screw 6 is screwed into a nut 1a welded to the bend portion 3a of the half ring-shaped member 3A.
When the manipulation lever 2 is pivoted about the screw 4 in an arrow-a direction in FIG. 9, the cam part of the manipulation lever 2 is pressed against the bent portion 3b2 of the half ring-shaped member 3B, and thus, the circumferential length of the fastening band 3 is decreased. Then, the fastening band 3 is fastened to an attachment shaft of a tool body 100 of, for example, a disc grinder, and thus, the wheel guard 1 is fixed.
When grinding an object material, it is necessary to adjust an acting portion of the tool bit (specifically, an acting position of the tool bit relative to the disc grinder body) according to the shapes of the object material, a portion to be ground in the object material, and a detail of the operation. When grinding the object material, the wheel guard 1 is fixed at the position as shown in FIG. 8A. When cutting the object material, the wheel guard 1 is fixed at the position as shown in FIG. 8B.
To adjust the relative position of the wheel guard 1 to the tool body 100 (the portion of the tool bit covered by the wheel guard 1), it is necessary to loosen the fastening of the wheel guard 1 and to rotate the wheel guard 1 around the attachment shaft of the tool body 100.
In this case, when the manipulation lever 2 is pivoted from the position (first position) as shown in FIG. 9 to a position (second position) about the screw 4 in the arrow-b direction, the pressing force of the fastening band 3 against the bent portion 3b2 by the cam part of the manipulation lever 2 is released. Then, the circumferential length of the fastening band 3 is increased and the fastening force of the fastening band 3 is released. As a result, the wheel guard 1 can be freely rotated around the attachment shaft.
In this way, the circumferential position of the wheel guard 1 is changed. Thereafter, when the manipulation lever 2 is pivoted about the screw 4 in the arrow-a direction to be positioned at the position shown in FIG. 9, the fastening band 3 is fastened again so that the wheel guard 1 is fixed at the changed position.
By the one-touch pivot operation of the manipulation lever 2, the wheel guard 1 can be easily fixed and released in a short time.
In some cases, the related-art wheel guard unit shown in FIG. 9 may be attached to the disc grinder body 100 to be used for cutting the object material X as shown in FIGS. 10A and 10B. In such a case, there is a possibility that the manipulation lever 2 comes into contact with the object material X as shown in FIG. 10A. In that case, the manipulation lever 2 may be caught at the object material X as shown in FIG. 10B, so that the manipulation lever 2 is released and the fastening force of the wheel guard 1 with respect to the tool body 100 becomes weak. As a result, the wheel guard is unintendedly rotated during operation, and thus, the operability deteriorates.
Generally, a wheel guard unit of a disc grinder as shown in FIG. 17 is known. In the wheel guard unit, a wheel guard 101 is attached to a disc grinder body by fastening a fastening band 103 with screws 106.
As shown in FIG. 18, a wheel guard unit of a disc grinder according to another related art is illustrated. The wheel guard unit is provided with a position adjustment mechanism, in which a fulcrum shaft 104 of a lever 102 is fixed to a wheel guard 101 by means of a screw pin 105, and is attached to a disc grinder body.
Generally, when a disc grinder switches from a grinding operation in which a grindstone is attached thereto as a tool bit to a cutting operation, as regulated by the Japanese Regulations for Industrial Safety and Health and the Japanese Structural Standard of Disc Grinder, it is necessary to switch from a wheel guard configured to cover a single surface of the grindstone to a wheel guard configured to cover both surfaces of the grindstone.
However, the wheel guard 101 shown in FIG. 17 is inconvenient to use because it is necessary to use a tool such as a plus driver to loosen the screws 106 in order to detach the wheel guard.
In the wheel guard holding structure using the lever 102 shown in FIG. 18, the fastening force of the wheel guard 101 with respect to a power tool body of, for example, a disc grinder, can be easily adjusted by merely operating the lever 102. Here, the dimensional difference of the fastening band 103 between when fastening and when loosening is maintained, and the lever 102 is used to decrease/increase the fastening force of the fastening band 103. However, it is difficult to secure a sufficient dimensional difference enough for the wheel guard 101 to be smoothly detached: because of the limitation in an elastic deformation amount of the fastening band 103. For this reason, similar to the wheel guard 101 shown in FIG. 17, it is inconvenient to use because it is necessary to loosen the screws 106 in order to detach the wheel guard 101, in addition to the operation of the lever 102.
Furthermore, in the related-art wheel guard unit shown in FIGS. 17 and 18, similar labors as the detachment are required when the wheel guard 101 is attached to the power tool body, and it is inconvenient to use.
The related-art disc grinders are shown in, for example, JP-H09-141551-A and JP-UM-H06-036764-A.